Lymphatic filariasis (LF) is a neglected tropical disease caused by parasitic nematodes, including Brugia malayi, which are transmitted through the bite of infected vector mosquitoes. The prevalence of LF is staggering; over 120 million people are infected, with over 1.2 billion at risk in 73 endemic countries. Despite coordinated elimination efforts, LF remains a significant global health concern and there is a recognized need for new strategies to control parasitic nematodes. Progress towards that goal is frustrated, however, because we simply do not have adequate understanding of parasite biology. For example, the interaction between mosquito and parasite during the B. malayi life cycle is delicately balanced and although the parasite manipulates the mosquito to create conditions favorable to parasitism, we know little about how they do this. Host-parasite interactions have long been promoted as novel intervention sites because any mechanism that disrupts the vector-parasite interaction and skews the balance in favor of the vector is likely to prevent infection, parasite development or transmission. This project represents an exciting new direction for investigating the vector-parasite interface. We propose that B. malayi can actively manipulate the mosquito host to the benefit of the parasite by using small, regulatory RNAs (microRNAs, miRNA) delivered via specialized packages called exosomes. In Specific Aim 1 of this application we will characterize exosome secretion by Brugia within the mosquito host and identify exosome cargo. Exosomes will be collected from mosquito-borne stage parasites and visualized, quantified and sized using electron microscopy and NanoSight tracking analysis. We will use deep sequencing techniques to characterize the small RNA cargo of the exosomes. Finally, we will use biomarkers and bioinformatics to reveal profile exosome secretion throughout complete parasite development in the mosquito vector. In Specific Aim 2 we will explore the function of these exosomes at the vector-parasite interface. We will inject mosquitoes with purified exosomes and discrete small RNA cargo, then monitor changes to normal vector biology using deep sequencing techniques. This will identify both novel and explicit parasite effector molecules and the vector pathways that are manipulated. Successful completion of this project will generate new knowledge of B. malayi biology fundamental to parasitism. Furthermore, the mechanisms exposed may apply to other parasitic nematodes as they manipulate their hosts, be they vectors, humans, livestock or indeed plants.